Various processes are repeatable, and thus lend themselves to real time process monitoring. An example of such a repeatable process is vibration welding, which involves the controlled application of high frequency vibration energy to a clamped work piece. Surface friction generates heat at a weld interface, which ultimately softens and bonds adjacent work piece surfaces at the interface. For a given work piece, the formation of each weld is often performed in a consistent, repeatable manner.
Conventional process control methods for repeatable processes monitor fixed variables against calibrated thresholds. That is, various closed-loop parameter-based control techniques may be applied to maintain certain weld parameters within calibrated limits. This approach can produce reasonably consistent welding parameters over time. However, stable welding process parameters may still fail to produce welds of a consistently high quality. In addition, external factors such as material quality can also impact weld quality. A premature failure of just one weld can affect the performance of a welded system. It is therefore common practice to determine weld integrity by visual inspection of each weld, followed by a labor intensive process known as picking, wherein each of the formed welds is physically tested by an operator using a picking tool.